This application is based on Japanese Patent Applications No. 11-4241 filed Jan. 11, 1999, No. 11-123604 filed Apr. 30, 1999 and No. 11-184816 filed Jun. 30, 1999, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a hydraulically operated braking system, and more particularly to a hydraulic pressure source apparatus for a hydraulically operated braking system.
2. Discussion of the Related Art
JP-A-2-169355 discloses a braking hydraulic pressure source apparatus including (1) a cylinder housing, (2) a pressurizing piston fluid-tightly and slidably received in the cylinder housing and cooperating with the cylinder housing to define a front pressurizing chamber and a rear assisting pressure chamber on respective front and rear sides of the pressurizing piston, the pressurizing piston being advanced in response to an operation of a brake operating member by an operator, to pressurize a working fluid in the front pressurizing chamber, and (3) an assisting pressure control device for controlling a pressure of the working fluid in said rear assisting pressure chamber (hereinafter referred to as xe2x80x9cassisting hydraulic pressurexe2x80x9d).
Where this braking hydraulic pressure source apparatus is used in a hydraulically operated braking system for an automotive vehicle, the working fluid in the rear assisting pressure chamber is pressurized to develop the assisting hydraulic pressure, so that the braking system performs a traction control for a drive wheel of the vehicle. Described in detail, the traction control is initiated without an operation of the brake operating member by the vehicle operator, with the assisting hydraulic pressure being applied to the rear assisting pressure chamber by the assisting pressure control valve, in response to a signal indicating an excessive amount of traction force acting on the drive wheel, so that the pressurizing piston is advanced to pressurize the working fluid in the front pressurizing chamber. As a result, the working fluid in the front pressurizing chamber pressurized by the pressurizing piston is supplied to a wheel brake cylinder connected to the front pressurizing chamber, so that the pressure of the working fluid in the wheel brake cylinder is increased for braking the drive wheel. The fluid pressure in the wheel brake cylinder is controlled by a pressure control valve device, so as to regulate the traction force of the drive wheel such that the amount of slip of the drive wheel on the road surface is held within an optimum range.
It is therefore a first object of the present invention to provide an improved braking hydraulic pressure source apparatus having an assisting pressure chamber as described above.
A second object of this invention is to provide a hydraulically operated braking system equipped with such an improved braking hydraulic pressure source apparatus.
The first or second object indicated above may be achieved by any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, so as to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A braking hydraulic pressure source apparatus comprising: a cylinder housing; a pressurizing piston fluid-tightly and slidably received within the cylinder housing and cooperating with the cylinder housing to define a front pressurizing chamber and a rear assisting pressure chamber on respective front and rear sides of the pressurizing piston, the pressurizing piston being advanced in response to an operation of a brake operating member, to pressurize a working fluid in the front pressurizing chamber; and an electrically controlled assisting pressure control device for controlling an assisting hydraulic pressure which is a pressure of the working fluid in the rear assisting pressure chamber, such that a boosting ratio which is a ratio of an output of the pressurizing piston to an input of the pressurizing piston is controlled to be a predetermined value.
In the braking hydraulic pressure source apparatus, the pressurizing piston receives a primary drive force based on an operating force acting on the brake operating member, and an assisting drive force based on the assisting hydraulic pressure in the rear assisting pressure chamber. As a result, the pressurizing piston is advanced by a sum of these primary and assisting drive forces, and the working fluid in the front pressurizing chamber is pressurized to a value corresponding to the above-indicated sum. Where the brake operating member is directly connected to the pressurizing piston, the primary drive force is substantially equal to the operating force applied to the brake operating force by an operator. Where a booster is provided between the brake operating member and the pressurizing piston, the primary drive force is an output force of the booster which boosts the operating force applied to the brake operating member.
When the primary drive force is held constant, an increase of an assisting force by increasing the assisting hydraulic pressure results in an increase of the boosting ratio, and a reduction of the assisting force by reducing the assisting hydraulic pressure results in a reduction of the boosting ratio. Thus, the boosting ratio of the braking hydraulic pressure source apparatus can be controlled by controlling the assisting hydraulic pressure in the rear assisting pressure chamber. In the braking hydraulic pressure source apparatus according to the above mode (1) of this invention, the assisting hydraulic pressure is electrically controlled by the electrically controlled assisting pressure control device, such that the boosting ratio is controlled to be the predetermined value. This predetermined value may be either a constant value irrespective of the input and output of the pressurizing piston, or a variable which changes in steps or continuously depending upon the input and output of the pressurizing piston. In the present braking hydraulic pressure source apparatus, the boosting ratio is controlled to be the predetermined value. However, the principle of the present invention does not exclude a control of the boosting ratio depending upon the operating state of the brake operating member, the operating condition of a braking system for which the present braking hydraulic pressure source apparatus is used, and the running condition of an automotive vehicle on which the braking system is provided.
In the conventional braking hydraulic pressure source apparatus, the assisting hydraulic pressure is controlled while the braking system is performing a traction control for a drive wheel, without an operation of the brake operating member. However, the conventional braking hydraulic pressure source apparatus is not adapted to control the assisting hydraulic pressure during an operation of the brake operating member for effecting a normal braking operation. In the present braking hydraulic pressure source apparatus, the assisting hydraulic pressure is controlled at least during a normal braking operation of the braking system with an operation of the brake operating member. This is a departure from the conventional concept, based on a finding of a new application of the assisting pressure chamber for improved performance of the braking hydraulic pressure source apparatus.
As discussed above, the input of the pressurizing piston is boosted into its output by electric control of the assisting hydraulic pressure by the assisting pressure control device, so that the assisting pressure chamber as an assisting pressure chamber and the electrically controlled assisting pressure control device may be considered to provide an electrically controlled booster device. It is noted that the cylinder housing and the pressurizing piston may be a housing of a master cylinder and a pressurizing piston disposed in this master cylinder housing.
(2) A braking hydraulic pressure source apparatus according to the above mode (1), wherein the assisting pressure control device includes an output-pressure-dependent pressure control device for controlling the assisting hydraulic pressure in the rear assisting pressure chamber on the basis of a pressure of the working fluid in the front pressurizing chamber.
As described below in DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT, there is a predetermined relationship between the assisting hydraulic pressure and the pressure of the fluid in the front pressurizing chamber (hereinafter referred as xe2x80x9coutput hydraulic pressurexe2x80x9d of the pressurizing piston), in the braking hydraulic pressure source apparatus according to the above mode (1) of the present invention in which the boosting ratio is controlled to be the predetermined value. Where the predetermined value of the boosting ratio is a predetermined constant value, for instance, the output hydraulic pressure of the pressurizing piston has a proportional relationship with the assisting hydraulic pressure. Based on this proportional relationship and the output hydraulic pressure, the assisting hydraulic pressure can be controlled to establish the predetermined boosting ratio.
(3) A braking hydraulic pressure source apparatus according to the above mode (1) or (2), wherein the assisting pressure control device includes a pressure increasing and reducing device for increasing the assisting hydraulic pressure if the assisting hydraulic pressure is lower than a desired value corresponding to a pressure of the working fluid in the front pressurizing chamber, and reducing the assisting hydraulic pressure if the assisting hydraulic pressure is higher than the desired value.
When the assisting hydraulic pressure is higher than a desired value corresponding to the output hydraulic pressure of the pressurizing piston, the boosting ratio is lower than when the assisting hydraulic pressure is lower than the above-indicated desired value. Therefore, when the assisting hydraulic pressure is lower than the desired value, the boosting ratio can be increased toward the predetermined value by increasing the assisting hydraulic pressure. Conversely, when the assisting hydraulic pressure is higher than the desired value, the boosting ratio can be reduced toward the predetermined value by reducing the assisting hydraulic pressure. Thus, the boosting ratio can be controlled to be the predetermined value by increasing or reducing the assisting hydraulic pressure depending upon whether the assisting hydraulic pressure is lower or higher than the desired value which corresponds to the fluid pressure in the front pressurizing chamber or the output hydraulic pressure of the pressurizing piston.
(4) A braking hydraulic pressure source apparatus according to the above mode (3), wherein the assisting pressure control device further includes a pressure holding device for holding the assisting hydraulic pressure if the assisting hydraulic pressure is almost equal to the desired value.
When the assisting hydraulic pressure is almost equal to the desired value corresponding to the output hydraulic pressure of the pressurizing piston, the boosting ratio is almost equal to the predetermined value. In this instance, the assisting hydraulic pressure need not be increased or reduced, and is therefore held at the present value.
(5) A braking hydraulic pressure source apparatus according to the above mode (1) or (2), wherein the assisting pressure control device further includes a pressure increasing and reducing device for increasing the assisting hydraulic pressure if a pressure of the working fluid in the front pressurizing chamber is higher than a desired value by more than a predetermined first amount, and reducing the assisting hydraulic pressure if the pressure of the working fluid in the front pressurizing chamber is lower than the desired value by more than a predetermined second amount, the desired value being determined by an actual value of the assisting hydraulic pressure and the predetermined value of the boosting ratio.
When the output hydraulic pressure of the pressurizing piston is higher than the desired value determined by the relationship between the desired assisting hydraulic pressure and the predetermined value of the boosting ratio, the actual assisting hydraulic pressure is lower than its desired value, and the actual boosting ratio is lower than the predetermined desired value. When the output hydraulic pressure is lower than the desired value, the actual assisting hydraulic pressure is higher than the desired value. The boosting ratio can be changed toward the desired value by increasing the assisting hydraulic pressure when the output hydraulic pressure is considerably higher than the desired value, and reducing the assisting hydraulic pressure when the output hydraulic pressure is considerably lower than the desired value.
(6) A braking hydraulic pressure source apparatus according to the above mode (5), wherein the assisting pressure control device further includes a pressure holding device for holding the assisting hydraulic pressure if the pressure of the fluid in the front pressurizing chamber is in a range determined by the desired value thereof and the predetermined first and second amounts.
When the output hydraulic pressure of the pressurizing chamber is close to the desired value, the boosting ratio is almost equal to the predetermined desired value, and the assisting hydraulic pressure is held at the present value.
(7) A braking hydraulic pressure source apparatus according to any one of the above modes (1)-(6), wherein the assisting pressure control device includes an output-change-rate- dependent pressure control device for controlling the assisting hydraulic pressure on the basis of a rate of change of the pressure of the working fluid in the front pressurizing chamber.
The output hydraulic pressure of the pressurizing piston changes with an increase in the brake operating force applied to the brake operating member by the operator, if the assisting hydraulic pressure is held constant. The rate of change of the output hydraulic pressure changes with a rate of change of the brake operating force. Accordingly, by controlling the assisting hydraulic pressure on the basis of the rate of change of the output hydraulic pressure, the assisting hydraulic pressure is controlled according to the rate of change of the brake operating force, so that the actual boosting ratio of the braking hydraulic pressure source apparatus can be suitably controlled to approach the predetermined value.
Where the feature according to the above mode (7) is provided in the braking hydraulic pressure source apparatus according to any one of the above modes (3)-(6), the assisting hydraulic pressure is increased or reduced depending upon the rate of change of the output hydraulic pressure, namely, the pressure of the fluid in the front pressurizing chamber.
(8) A braking hydraulic pressure source apparatus according to any one of the above modes (1)-(7), wherein the assisting pressure control device includes an output-change-rate- dependent assisting pressure change rate control device for controlling a rate of change of the assisting hydraulic pressure on the basis of a rate of change of the pressure of the working fluid in the front pressurizing chamber.
When the assisting hydraulic pressure is controlled to change at a rate corresponding to a rate of change of the output hydraulic pressure, the assisting hydraulic pressure is changed at a rate corresponding to a rate of change of the brake operating force, so that the boosting ratio can be controlled with particularly high stability.
(9) A braking hydraulic pressure source apparatus according to any one of the above modes (1)-(8), wherein the assisting pressure control device includes an assisting pressure change rate control device for controlling a rate of change of the assisting hydraulic pressure such that the rate of change of the assisting hydraulic pressure is held at a predetermined constant value while the rate of change of the pressure of the working fluid in the front pressurizing chamber is held in a predetermined range, and such that the rate of change of the assisting hydraulic pressure changes with the rate of change of the pressure in the front pressurizing chamber while the rate of change of the pressure of the working fluid in the front pressurizing chambers is not in the predetermined rate.
In the braking hydraulic pressure source apparatus according to the above mode (9), the rate of change of the assisting hydraulic pressure is held at a predetermined constant value if the rate of change of the output hydraulic pressure is in a predetermined range, for instance, in a range higher than a predetermined first positive value or lower than a predetermined second positive value. One example of the latter case will be described below with respect to the mode (10) of this invention. In one example of the former case, the rate of change of the assisting hydraulic pressure while the rate of change of the output hydraulic pressure is higher than the predetermined first positive value is made lower than a value which corresponds to the rate of change of the pressure of the fluid in the front pressurizing chamber. The rate of change of the assisting hydraulic pressure may be made constant where the. rate of change of the output hydraulic pressure is in a predetermined range higher than a predetermined third negative value or lower than a predetermined fourth negative value.
Where the feature according to the above mode (9) is provided in the braking hydraulic pressure source apparatus according to any one of the above modes (3)-(6), the rate of change of the assisting hydraulic pressure while the rate of change of the output hydraulic pressure is not in the predetermined range is controlled on the basis of the rate of change of the output hydraulic pressure.
(10) A braking hydraulic pressure source apparatus according to the above mode (9), wherein the rate of change of the assisting hydraulic pressure while the rate of change of the pressure of the working fluid in the front pressurizing chamber is lower than a predetermined value is made higher than a value which corresponds to the rate of change of the pressure of the working fluid in the front pressurizing chamber.
In the braking hydraulic pressure source apparatus according to the above mode (10), the rate of change of the assisting hydraulic pressure while the rate of change of the output hydraulic pressure is lower than a predetermined value is made higher than a value which corresponds to the rate of change of the output hydraulic pressure, the assisting hydraulic pressure can be changed so as to cause the boosting ratio of the braking hydraulic pressure source apparatus to approach the predetermined value, even if the rate of change of the output hydraulic pressure is relatively low.
Where the feature according to the above mode (10) is provided in the braking hydraulic pressure source apparatus according to any one of the above modes (4)-(6), the assisting hydraulic pressure is changed at the predetermined rate so that the boosting ratio is rapidly changed toward the predetermined value, even when the output hydraulic pressure is changed at a relatively low rate. Accordingly, the operation to increase or reduce the assisting hydraulic pressure can be rapidly changed into the operation to hold the assisting hydraulic pressure. That is, even while the input force applied to the pressurizing piston is increased considerably slowly, the assisting hydraulic pressure can be efficiently controlled to be held at a constant value corresponding to the predetermined value of the boosting ratio. Accordingly, frequent operations to increase and reduce the assisting hydraulic pressure before the predetermined boosting ratio has been reached can be avoided.
(11) A braking hydraulic pressure source apparatus according to any one of the above modes (1)-(10), wherein the assisting pressure control device comprises an electrically operated hydraulic power source including a hydraulic pump connected to the rear assisting pressure chamber, and an electric motor for driving the hydraulic pump.
In the braking hydraulic pressure source apparatus according to the above mode (11), the pressurized fluid is delivered from the hydraulic pump to the rear assisting pressure chamber to increase the assisting hydraulic pressure.
Where the electrically operated hydraulic power source is arranged such that the rate of flow of the pressurized fluid delivered from the hydraulic pump is controllable, the rate of increase of the assisting hydraulic pressure in the rear assisting pressure chamber can be controlled by controlling the electrically operated hydraulic pressure source apparatus. Where the electrically operated hydraulic power source is arranged so as to suitably permit the fluid flows into and from the rear assisting pressure chamber, the assisting hydraulic pressure can be increased or reduced by controlling the valve device. In this latter case, the hydraulic pump may be a gear pump, whose rotating directions are suitably selected so as to permit the fluid flows into and from the rear assisting pressure chamber.
(12) A braking hydraulic pressure source apparatus according to any one of the above modes (1)-(11), wherein the assisting pressure control device comprises a pressure control valve device including (a) a solenoid-operated pressure control valve for controlling the assisting hydraulic pressure in the rear assisting pressure chamber according to an electric current to be applied to the pressure control valve, and (b) a current control device for controlling the electric current to be applied to the solenoid-operated pressure control valve.
In the pressure control valve device provided according to the above mode (12), the assisting hydraulic pressure in the rear assisting pressure chamber can be controlled by controlling the electric current to be applied to the solenoid-operated pressure control valve. The pressure control valve may be either a shut-off valve which is selectively opened and closed with its solenoid coil being energized and de-energized so as to control the assisting hydraulic pressure, or a variable flow control valve adapted to control the rate of the fluid flow to the rear assisting pressure chamber depending upon the electric current applied to the solenoid coil. The pressure control valve device may include a plurality of solenoid-operated valves.
In either case, the feature according to the above mode (12) is preferably provided with the feature according to the above mode (11). Where the assisting hydraulic pressure is controllable by controlling the electric current to be applied to the solenoid-operated pressure control valve, the electrically operated hydraulic power source may be constructed to be simply able to deliver the pressurized fluid to the rear assisting pressure chamber at a constant flow rate, so that the cost of manufacture of the electrically operated hydraulic pressure source apparatus can be reduced. Since the assisting hydraulic pressure in the rear assisting pressure chamber can be increased by the pressurized fluid delivered from the hydraulic pump, the assisting hydraulic pressure can be controlled by providing the pressure control valve device with a single pressure reducing valve for reducing the assisting hydraulic pressure. In this case, the pressure control valve device using the single pressure reducing valve is available at a reduced cost.
(13) A braking hydraulic pressure source apparatus according to the above mode (12), wherein the solenoid-operated pressure control device includes a housing having a valve seat, a valve member movable toward and away from the valve seat, and an electromagnetic force generating device for generating an electromagnetic force acting on the valve member, depending upon an electric current to be applied to the electromagnetic force generating device, and wherein the current control device includes a device for increasing the electric current to be applied to the electromagnetic force generating device, at a predetermined rate while the rate of increase of the pressure of the working fluid in the rear assisting pressure chamber is lower than a predetermined lower limit.
In the solenoid-operated pressure control valve, the assisting hydraulic pressure may not be increased with an increase in the electric current applied to the electromagnetic force generating device, if the amount of increase of the electric current per each control cycle is considerably small. In view of this tendency, the amount of increase of the electric current per each control cycle is kept at a predetermined value as long as the rate of increase of the output hydraulic pressure is lower than the predetermined lower limit. That is, the amount of increase of the electric current is changed with an increase in the rate of increase of the output hydraulic pressure only while the rate of change of the output hydraulic pressure is not lower than the lower limit. According to this arrangement, the assisting hydraulic pressure can be changed even when the input force applied to the pressurizing piston is increased at a considerably low rate. The current control device may be adapted to reduce the electric current at a predetermined rate while the rate of reduction of the pressure of the working fluid in the rear assisting pressure chamber is lower than a predetermined lower limit.
The solenoid-operated pressure control valve may be a normally open valve or a normally closed valve. For instance, the solenoid-operated pressure control valve may be a normally open valve including a valve seat, a valve member, a spring for biasing the valve member in a direction for holding the valve member apart from the valve seat, and an electromagnetic forge generating device which generates an electromagnetic force corresponding to the electric current, such that the electromagnetic force acts on the valve member in a direction for moving the valve member toward the valve seat, as described below with respect to the presently preferred embodiment of this invention. Where this normally open solenoid-operated pressure control valve is disposed between the rear assisting pressure chamber and a reservoir, this valve functions as a pressure reducing valve for reducing the assisting hydraulic pressure in the rear assisting pressure chamber.
(14) A braking hydraulic pressure source apparatus according to any one of the above modes (1)-(13), further comprising a mechanically controlled booster interconnected between the brake operating member and the pressurizing piston, for boosting an operating force acting on the brake operating member, the booster having a mechanically operated control valve for controlling a pressure of a fluid by which the operating force is boosted so that the boosted operating force is applied to the pressurizing piston.
In the braking hydraulic pressure source apparatus according to the above mode (14), the output force of the mechanically controlled booster is the input to the pressurizing piston. The mechanically controlled booster is distinguished from an electrically controlled booster, which is provided in the braking hydraulic pressure source apparatus according to any one of the above modes (1)-(13). That is, the electrically controlled booster is constituted by the pressurizing piston and the electrically controlled assisting pressure control device adapted to control the assisting hydraulic pressure in the rear assisting pressure chamber formed on the rear side of the pressurizing piston. The mechanically controlled booster may be a vacuum booster or a hydraulic booster as well known in the art. In the braking hydraulic pressure source apparatus according to the above mode (14), the mechanically controlled booster and the electrically controlled booster are disposed in series connection with each other between the brake operating member and the pressurizing piston, so that the operating force applied to the brake operating member by the operator is boosted by both of the mechanically and electrically controlled boosters. Therefore, the overall boosting ratio of this pressure source apparatus can be made higher than the boosting ratio of a pressure source device using only the mechanically controlled booster, in particular, a vacuum booster. Further, the present apparatus can be comparatively easily adapted to provide the desired boosting characteristic.
(15) A braking hydraulic pressure source apparatus according to any one of the above modes (1)-(14), wherein the assisting pressure control device includes a device for initiating an operation to control the assisting hydraulic pressure in the rear assisting pressure chamber when the pressure of the working fluid in the front pressurizing chamber has been increased to a predetermined control initiating threshold value.
In the braking hydraulic pressure source apparatus, the operation of the assisting pressure control device is initiated when the fluid pressure in the front pressurizing chamber has been increased to the predetermined control initiating threshold value. Where the mechanically controlled booster described above with respect to the above mode (14) is provided, the assisting pressure control device is activated when the fluid pressure in the front pressurizing chamber has been increased to a value which is to be detected when the boosting limit of the booster has been reached. However, the threshold value may be higher or lower than the above-indicated value corresponding to the boosting limit. The threshold value may be zero. In this case, the operation of the assisting pressure control device to control the assisting hydraulic pressure is initiated when the brake operating member is operated by the operator.
(16) A braking hydraulic pressure source device according to any one of the above modes (1-15, wherein the assisting pressure control device includes a pressure control mode selecting portion for selecting a pressure increase mode when the assisting hydraulic pressure is lower than a desired value corresponding to the pressure of the working fluid in the front pressurizing chamber, a pressure reduction mode when the assisting hydraulic pressure is higher than the desired value, and a pressure hold mode when the assisting hydraulic pressure is almost equal to the desired value, the assisting pressure control device further including a pressure control portion for increasing and reducing the assisting hydraulic pressure when the pressure increase and reduction modes are selected, respectively, so that the pressure increase and reduction modes are changed to the pressure hold mode, the pressure control portion reducing the assisting hydraulic pressure when the pressure reduction mode is selected.
(17) A braking hydraulic pressure source apparatus comprising: a cylinder housing; a pressurizing piston fluid-tightly and slidably received with in the cylinder housing and cooperating with the cylinder housing to define a front pressurizing chamber and a rear assisting pressure chamber on respective front and rear sides of the pressurizing piston, the pressurizing piston being advanced in response to an operation of a brake operating member, to pressurize a working fluid in the front pressurizing chamber; and an electrically controlled assisting pressure control device for controlling an assisting hydraulic pressure which is a pressure of the working fluid in the rear assisting pressure chamber, such that a boosting ratio which is a ratio of an output of the pressurizing piston to an operating force acting on the brake operating member.
In the braking hydraulic pressure source apparatus according to the above mode (17), the application of the brake operating force (operating force acting on the brake operating member) to the pressurizing piston is not essential. That is, the assisting pressure control device may be adapted to control the assisting hydraulic pressure on the basis of the brake operating force as detected by a suitable force sensor. In this case, the fluid pressure in the rear pressurizing chamber is increased to produce a braking force, as if the brake operating force actually applied to the pressurizing piston were boosted at the predetermined boosting ratio.
(18) A braking hydraulic pressure source apparatus comprising: a cylinder housing; a pressurizing piston fluid-tightly and slidably received with in the cylinder housing and cooperating with the cylinder housing to define a front pressurizing chamber and a rear assisting pressure chamber on respective front and rear sides of the pressurizing piston, the pressurizing piston being advanced in response to an operation of a brake operating member, to pressurize a working fluid in the front pressurizing chamber; and an electrically controlled assisting pressure control device for controlling an assisting hydraulic pressure which is a pressure of the working fluid in the rear assisting pressure chamber, on the basis of an amount of operation of the brake operating member.
In the braking hydraulic pressure source apparatus according to the above mode (18), the assisting hydraulic pressure in the rear assisting pressure chamber is controlled depending upon an amount of operation of the brake operating member by an operator. The amount of operation of the brake operating member may be represented by an operating stroke of the brake operating member, or an operating force acting on the brake operating member.
(19) A braking system for braking a wheel of an automotive vehicle, comprising: a braking hydraulic pressure source apparatus according to any one of the above modes (1)-(18); a wheel brake cylinder connected to said front pressurizing chamber of said braking hydraulic pressure source apparatus and operable for braking the wheel; and an independent pressure control device for controlling a pressure of the working fluid in said wheel brake cylinder, independently of the pressure of the working fluid in said front pressurizing chamber, and wherein the braking hydraulic pressure source apparatus includes an assisting pressure control pump connected to the rear assisting pressure chamber, and the independent pressure control device includes a reservoir for storing the working fluid discharged from the wheel brake cylinder, an independent pressure control pump for pressurizing the working fluid received from the reservoir, and an electric motor for driving the independent pressure control device, the electric motor being also used by the braking hydraulic pressure source apparatus, for driving the assisting pressure control pump.
The braking system according to the above mode (19) wherein the single electric motor is used for driving the assisting pressure control pump and the independent pressure control pump is available at a lower cost than a braking system wherein the two pumps are driven by respective electric motors.
(20) A braking system for braking a wheel of an automotive vehicle, comprising: a braking hydraulic pressure source apparatus including a (1) a cylinder housing, (2) a pressurizing piston fluid-tightly and slidably received within the cylinder housing and cooperating with the cylinder housing and cooperating with the cylinder housing to define a front pressurizing chamber and a rear assisting pressure chamber on respective front and rear sides of the pressurizing piston, the pressurizing piston being advanced in response to an operation of a brake operating member, to pressurize a working fluid in the front pressurizing chamber, and (3) an assisting pressure control pump connected to the rear assisting pressure chamber; a wheel brake cylinder connected to the front pressurizing chamber of the braking hydraulic pressure source apparatus and operable for braking the wheel; and an independent pressure control device for controlling a pressure of the working fluid in the wheel brake cylinder, independently of the pressure of the working fluid in the front pressurizing chamber, and wherein the independent pressure control device includes a reservoir for storing the working fluid discharged from the wheel brake cylinder, an independent pressure control pump for pressurizing the working fluid received from the reservoir, and an electric motor for driving the independent pressure control device, the electric motor being also used by the braking hydraulic pressure source apparatus, for driving the assisting pressure control pump.
In the braking system according to the above mode (20), the independent pressure control pump and the assisting pressure control pump are both driven by the same electric motor, and the cost of manufacture of the braking system having the rear assisting pressure chamber is made lower than that of a braking system wherein two electric motors are used to drive the respective two pumps. In this sense, the present braking system is an improvement over a braking system of the type as disclosed in JP-A-2-169355. The electric motor preferably has a capacity enough to permit simultaneous operations of the independent pressure control pump and the assisting pressure control pump.
The independent pressure control device may be adapted to include at least one of (a) an anti-lock braking pressure control device for controlling the fluid pressure in the wheel brake cylinder during an operation of the brake operating member such that the amount of slipping of the wheel is held in an optimum range, (b) a traction control device for controlling the fluid pressure in the wheel brake cylinder while the brake operating member is not in operation and while the wheel to be braked by the wheel brake cylinder is driven for running the automotive vehicle, such that the amount of slip of the drive wheel is held in an optimum range, and (c) a vehicle running stability control device for controlling the fluid pressure in the wheel brake cylinder to brake the wheel so as to increase the running stability of the vehicle.
The braking hydraulic pressure source apparatus in the braking system according to the above mode (20) may include any one of the technical features which have been described above with respect to the above modes (1)-(18).
(21) A braking system according to the above mode (19) or (20), wherein the braking hydraulic pressure source apparatus includes an assisting pressure control device for controlling an assisting hydraulic pressure which is a pressure of the working fluid in the rear assisting pressure chamber, by using the pressurized fluid delivered from the assisting pressure control pump, the braking system comprising an interference preventing device which permits an operation of the assisting pressure control device to control the assisting hydraulic pressure in the rear assisting pressure chamber and an operation of the independent pressure control device to control the pressure of the working fluid in the wheel brake cylinder, without an interference between the controls of the pressure in the rear assisting pressure chamber and the wheel brake cylinder by the assisting pressure control device and the independent pressure control device.
In the braking system according to the above mode (21), the control of the fluid pressure in the wheel brake cylinder by the independent pressure control device and the control of the assisting hydraulic pressure in the rear assisting pressure chamber by the assisting pressure control device can be effected without an interference with each other. For instance, the assisting pressure control device includes a pressure control valve which is capable of controlling the assisting hydraulic pressure without influencing the wheel brake cylinder pressure controlled by the independent pressure control device. The assisting pressure control pump may be kept operated even while the control of the assisting hydraulic pressure is unnecessary during an operation of the independent pressure control device to control the wheel brake cylinder pressure. In this case, the pressure control valve of the assisting pressure control device may be controlled to prevent an increase in the assisting hydraulic pressure in the rear assisting pressure chamber. Thus, the assisting pressure control device including the pressure control valve makes it possible to permit the controls of the assisting hydraulic pressure and the wheel brake cylinder pressure without an interference with each other. In this case, the pressure control valve may be considered to be the interference preventing device indicated above. The independent pressure control pump is kept operated even while the wheel brake cylinder pressure is not being controlled, as long as the assisting hydraulic pressure is being controlled, that is, as long as the electric motor is operated to drive the assisting pressure control pump. However, the independent pressure control pump may be adapted to be run without an actual pumping action when no fluid is stored in the reservoir as a result of the discharge flow of the fluid from the wheel brake cylinder into the reservoir. This arrangement prevents a control of the wheel brake cylinder pressure by the independent pressure control pump. In this case, the independent pressure control device which is run without an actual pumping action when no fluid is stored in the reservoir can be considered to be the interference preventing device.